Every week, the BBC Focus magazine solves some doubts of its readers. Below is a selection of their responses for the curious.
What is the biggest butterfly in the world?
Several species dispute the title. The Queen Alexandra Birdwing (Ornithoptera alexandrae) is considered the world’s largest diurnal butterfly with a wingspan (distance between wingtips) of up to 31cm. It is in danger of extinction and is found in Papua New Guinea, Indonesia.
Among the moths, the largest by wingspan is the Monarch. (Thysania agripinade), which can also reach up to 31cm. It is found mainly in Mexico, Central America, and South America.
For its part, the Atlas butterfly (Attacus Atlas), also nocturnal, is the largest taking into account the total area of its wings (more than 400cm2). Its wingspan is between 25cm and 30cm. It is found in Southeast Asia, China, the Malay Archipelago, and Indonesia.
Do cataracts affect iris recognition systems?
Not in theory. Iris recognition systems use an algorithm to match the unique pattern of your iris. A cataract is the total or partial opacification of the lens, another part of the eye.
A 2004 study showed that cataract surgery can confuse technology, but a subsequent report in the journal Nature suggested that the intervention has no effect.
The report added, however, that iris recognition systems could be circumvented if the iris is dilated using eye drops.
What causes addiction?
Addictive drugs interfere with neurotransmitters, the chemicals that transmit signals throughout the brain, and their receptors.
This causes changes in the brain’s reward system. It can create cravings and tolerance such that a higher dose is needed to have the same effect.
Some drugs also produce an unpleasant withdrawal syndrome that only eases when the person uses more.
Heroin is the most addictive drug known. It mimics the brain’s own endorphins, the natural opiates that induce pleasure and reduce pain.
The brain responds by reducing the number and sensitivity of its opioid receptors, causing the person to need more of the drug.
How are airplanes protected from lightning strikes?
The metallic fuselage of an airplane is, effectively, a Faraday Cage (an effect by which the electromagnetic field inside a balanced conductor is null and cancels out the effect of external fields), safely moving the current from the place where it impacts the beam until its exit.
However, lightning can potentially induce secondary currents in the wiring under the fuselage.
So for added protection the wiring and computers are electrically monitored.
The latest planes, like the Boeing 787 Dreamliner, are made of less conductive composite materials. Conductive fibers are woven into the fuselage to guide the beams safely through the body of the aircraft.